Process of producing organic cellulose ester molding powders and product thereof



Feb. 12, 1935. D. E. NORTHRUP ET AL 1,991,115

PROCESS OF PRODUCING ORGANIC CELLULOSE ESTER MOLDING POWDERS AND PRODUCTTHEREOF Filed July 17, 1931 syel'i 'equenqyCw've. i mam-111010111 Averammesgaaqesm Dennisl'l. I

- gwuanlfoug g W-M ducing cellulose acetate molding powders. It'

also relates to methods of producing powders com-- Patented Feb. 12,1935

1 1,991,115 v rnocnss or rnonuomo oncmc CELLU- LOSE ESTER MOLDINGPOWDEBS AND PRODUCT THEREOF Dennis E. Northrup and Amos W. Crane,Kingsport, Tenn, assiznors to Eastman Kodak Comig ani', Rochester, N.Y., a corporation of New Application July 17, 1931, Serial No. 551,508

10 @laims. (Cl. 106-40) This invention relates to the production ofcellulose organic esters in the form or finely divided, granular powderssuitable for molding purposes and more particularly to methods ofproprising plasticized or unplasticized organic esters of cellulosewhich may be converted to molding compositions.

It is a matter of common knowledge that cellulose acetate may beprecipitated irom its acetic acid or acetone solution by the addition ofwater in excess, cellulose acetate itself being insoluble in water. Thematerial thus produced, especially when precipitated at the normal rangeof atmospheric temperaturesis not as desirable as the molding powder ofour invention.

.Even though it is possible to precipitate cellulose acetate fromsolution in the form or light flakes or shreds, it is not suitable formolding operations. For practically all molding purposes the materialmust be in s; finely divided, granular, yet porous, form. Our inventionfulfills these requirements and makes cellulose acetate avail. able ase. molding powder in a highly desirable form which, due to the open orporous character or its particles, readily occludcs or absorbsplasticizers. The same holds true with respect to other organic estersof cellulose which may he produced in a similar fine, cronider, butporous, condition.

- The principal object of our invention is to provide ainethod ofproducing organic esters oi? cellulose in a finely divided, granular butporous form suitable for use in molding operations. A further object isto provide a simple method oi producing cellulose acetate and othercellulose organic ester molding powders having a piss tlcizerincorporated therein and being in a form which is available without,further treatment, for molding purposes. A still further object is toimprove upon known processes of precipitating cellulose acetate by theuse of certain specific types oi precipitating agents not heretoforeknown or used for this purpose. A specific ob loci; of the invention isto provide an improved method of producing a molding powder consist, ingof mixed higher fatty acid esters of cellulose.

These objects areaccomplished by the following invention which includesseveral methods of precipitating the finely divided granular moldingmaterial, although the same basic idea is present in each of them. Theessential features of our invention maybe said to comprise the formationoi a solution or dope of cellulose acetate,

cellulose acetate propionate, cellulose propionate or butyrate,cellulose acetate butyrate, cellulose acetate stearate or other organicester and the precipitation of the ester from its solution by adding anorganic precipitant followed by removal oi both solvent and precipitantby evaporation or filtration. In-the preferred form of the invention aplasticizer is incorporated into the product by adding it to the este:dope before precipitation and; in that modification in which theprecipitated cellulose acetate is separated from the solvents byfiltration, a silfficient amount oi plasticizer is added to the originalmixture to provide for a. proper quantity being retained by theprecipitated esters after filtration to give it the desired qualities.

Taking the production of cellulose acetate molding powder asillustrative, in corryingout our process we first make up a dope bydissolving the proper amount oi cellulose organic ester and plasticizerin acetone or other solvent. ,The solvent will, of course; hesclectedwith reference to its solvent power for the particular ester treated. Vin me manner the selection of the precipitant will depend upon theparticular com: pounds dealt with. ll. sufidcient amount oi a suitablenon solvent for the cellulose acetate, such as toluene is added rapidlyto entirely precipitate the cellulose acetate or an amount of theconcealment, such as toluene, is added which will merely produce jellingoi the acetate iollcwine which an additional amount of the nou -solventis added, with or without the addition or water, to complete theprecipitation. We also ilnd it possible tc'prcoluce a high grade densecellulose acetate molding" powder with suitable plasticizers intimatelycombined therewith Toy adding the de-= sired plasticizer in suitableproportions to the acetone dope :iollowed by the addition oi an agentwhich, while not truly s. precipitant in every respect (sometimes calleda swelling agent), is suficient oi a non-solvent under ordinaryconditions or temperature and pressure to act as a precipitant whenadded in sumciently large eacees. In this case we remove both thesolvent as well as the quasi-precipitant by distillation at eitheratmospheric or reduced pressure the same as with a true precipitant.This latter operationis normally carried out under practicallyarihydrous conditions, by simple distillation, in some cases it may bedesirable to remove the solvent and other agents by steam distillation,although this method is more'expenslve in that it necessitates thesubsequent dehydration of the solvent. 1 v

In either method we may remove the solvent and precipitant by filteringthe precipitated acetate from the mixture, followed by drying of thepowder. In using this method it is necessary to add the plasticizer tothe dope in sufficient quantity to leave. in the precipitated acetatesuch an amount of plasticizer as will give the finished product thedesired characteristics. In other words, the concentration of theplasticizer in the. common solvent should be higher than in the methodinvolving evaporation.

When it is desired to produce a molding pow- .der from a mixed celluloseester such as cellulose acetate stearate or cellulose acetatepropionate, the same general method may be employed, but it is necessaryin some instances to use special precipitants and in some cases toemploy a slightly different technique. It must be noted here thatalcohols higher in the series than ethyl alcohol will not ordinarilygive satisfactory results.

In the following examples we have set forth sever of the preferredembodiments of our invention which are included merely for purposes oiillustration and not as a limitation Earample I .l0 grams of acetonesoluble cellulose acetate are dissolved in 6.0 grams of acetone at roomtemperature; 10 grams of water are added to this solution. This does noteffect pre cipitation but merely economizes the toluene as an acetonesolution of cellulose acetate will normally tolerate some water. About200 c. c. of to1-' uene is then added with thorough agitation. Thecellulose acetate thereupon precipitates from the solution in a dense,finely divided powder which is very chalky and resembles wheat fiour inappearance, readily absorbs plasticizers and is an excellent moldingmaterial.

Example II.-A cellulose acetate dope is made up as in Example I, andsufficient toluene is then added to produce jelling of the acetate. Atthis point sufficient water is added in small quantities to initiateprecipitation of the acetate and this is followed by further additionsof toluene or water to complete the precipitation. As in Example I theproduct has physical characteristics and appearance satisfactory forsome purposes although large proportions of water and low temperaturesof precipitation are to be avoided as otherwise a horny product is aptto result.

Example III. grams of cellulose acetate are dissolved in 400 grams ofacetone. To the solution is added 30 grams of either dimethyl or diethylphthalate as a plasticizer. While stirring the resulting dope, 1200 c.c. of toluene is added at room temperature whereupon precipitation ofthe acetate in finely divided form occurs. The whole mass while stillbeing stirred is then warmed and the acetone and toluene aresuccessiyely removed and condensed by distillation. The resulting drypowder is very chalky, extremely finely divided and easily molded.Example IV .As an example of the production of a molding. powder from amixed organic ester of cellulose, a iven amount of cellulose acetatestearate containing 40% stearyl is dissolved in 6 parts of acetone. 10parts of methyl alcohol is then added with high speed stirring. Theresulting precipitation brings down a dense, finely di-= vided powderwhich filters and washes readily. Plasticizers may be incorporated ifdesired by dissolving them in the acetone solution of the-ester andsubsequently removing the solvent and premately 18% propionyl wasdissolved in 200 c. c. of acetone and 450 c. c. of carbon tetrachloridewas added with vigorous stirring. This addition of the carbontetrachloride produced a jelling of the cellulose acetate propionatewhereupon the mixture was diluted by further additions of carbontetrachloride until a total of 1000 c. 0. had been added. The jelledmaterial was thereby reduced "to a condition where filtration was easilyaccomplished. The precipitate was washed with 500 c. c.

more of carbon tetrachloride, dried, and the resulting product was afinely divided white powder. Example VI.--100 c. c. of a dope made up asin Example V was treated by the addition of 300 c. c. of butyl alcoholwith vigorous stirring. The resulting precipitated product was found tobe easily filterable and upon washing with 200 c. c. of butyl alcoholproduced an excellent, finely divided powder suitable for moldingpurposes. 1

Example VII.--100 c. c. of the acetate propionate dope of Example V wastreated by the addition of 300 c. c. of iso-propyl ether under theeonditions of Example VI'. In this case the precipitate required washingwith only 100 c. c.- of the precipitant toproduce the cellulose acetatepropionate in the desired finely divided'condition.

Example VIII .To 100 c. c. of a dope made up as in Example V was rapidlyadded'l50 c. c. of trichlorethylene which produced a gel. Upon theaddition of 200 c. c. more of. the trichlorethylene the celluloseacetate propionate precipitated in a finely divided form which, uponwashing with 250 c. c. of the precipitant gave a satisfactory powder. Asindicated, acetone is rather a universal soi vent for most organicesters of cellulose and it can rather generally be employed. Ethylenechloride is a solvent for the majority of the organic esters ofcellulose containing an acid radical higher than acetic. Propylenechloride is also a solvent for most of the higher mixed and singleorganic esters of cellulose. Numerous others are known to those skilledin the art and published in the literature and need not here berepeated. It is sufficient for the purposes of our invention to statethat the particular solvent will be selected with reference to thesolubility therein of the specific esters involved. With regard toprecipitants, we have found that these agents must be selected with alittle more care than in the case of solvents, and no broad general rulecan be laid down which will apply to all cases. We may, however, statedefinitely that the precipitants best suited to our purpose arenon-aqueous organic liquids which are also non-solvents for thecellulose organic ester.

Among these compounds which we have found to be good precipitants forcellulose acetate from acetone solutions may be included benzol,tolubutyl alcohol, amyl acetate, -trichlorethylene.

butoxy ethyl alcohol, and propylene chloride may be employed asprecipitants for cellulose acetate under certain circumstances. It haslikewise been discovered that trlchlorethylene, butyl alcohol,iso-propyl ether, and butoxy ethyl alcohol may be employed asprecipitants for cellulose acetate propionate under proper conditions.It

may be mentioned that when precipitating cellulose acetate propionatewith these compounds the ester is first produced in the form of a'jellwhich,-

after addition oi. the excess of the precipitating agent, goes over to afinely divided form which produce excellent results asprecipitants asdescribed and claimed in theapplication Serial No. 565,829 of C. J. Malmand J. D. Coleman, Jr. A

typical example of ,a precipitant which will 'precipitate all organicesters of cellulose from solution is iso-propyl ether, as described inthe application Serial No. 553,646 of C. J. Malm and C. R. Fordyce.

The selection of both solvents and precipitants depends to aconsiderable extent upon the solubility or insolubility, as the case maybe, of the particular ester which it is desired to produce in the formof a molding powder. of precipitant used will also vary for differentesters, especially in the case of those esterswhich are initiallyjelled'by the action of the precipitant but which, upon the addition ofan excess of the precipitant, are produced in the form of a finelydivided granular powder. It is also necessary to take into considerationthat the precipitating efiect of certain non-solvents is considerablyaifected by the character of the solvent with which it may be used. Inother words, when pre cipitating from a given ester solution, it will benecessary to use a precipitant such that, when added to the solution,its power to precipitate the ester will not be adversely afiected by'theformation of a binary solvent for the ester. Much of this generalcharacter of information is already known to those skilled in thecellulose derivative art and from the foregoing examples it will beapparent that a wide selection oi. solvents and non-solvents for thevarious organic esters of cellulose are available. Which particularsolvent or precipitant shall-be employed with any given organic ester ofcellulose can, from the above teachings, be quickly determined in thesame manner that one skilled in the art would determine any otherphysical characteristic of a product.

As one of the features of our invention, we have discovered that thereis a quite definite relation between the particle size of the productand the temperatureoi the solution in which precipitation takes place.We have found that, in general when employing organic precipitants, thelower the temperature, the smaller the particle size.

- Referring to the drawing, which shows a curve plotted from dataobtained in the precipitation or cellulose acetate from a azlacetonedope with toluene it may be seen that when the precipitation is carriedout at a temperature of approximately 41* C. the resulting powder willpass a lo-mesh screen, while if the temperature be lowered to 11 C. thematerial will pass a 200-mesh screen. Somewhat varied results will, ofcourse, obtain with other single and mixed organic esters of cellulosebut the broad teaching of. temperature control as a means for regulatingthe size of the precipitated particle applies to theother organic estersof cellulose as well..

We have also found that the composition of the mixture in whichprecipitation takes place has a pronounced eiiect upon the completenessof the precipitation of the ester. We have found that as the ratio oftoluene, for instance, increases, the more nearly does the precipitationThe amount approach completeness. The following table shows theresultsobtained with several types of cellulose acetate:

Percent. cellulose acetate precipitated from a 4:1 acetone solution Theabove tabulation indicates that with most acetates a little more than50% toluene .is satis-.- factory and.60-65% should be sufiicient toinsure substantially complete precipitation. If a larger proportion isnecessary for any particular conditions or. esters it will be quiteapparent from the teaching herein, in what manner this may becontrolled.

The product of our invention is characterized and; distinguished fromknown materials of this general class by the fact that it is anextremely finely divided, granular powder, the individual particles ofwhich are nevertheless of a light flufiy and porous naturewhich readilypermits the thorough incorporation of plasticizer. When producing ourmolding powder in a plasticized condition the precipitant is of courseselected with reference to its solvent action on the plusticizer and itsnon-solvent action upon the cellu-' lose acetate or other celluloseorganic ester in volved. Since the particles of the ester alwaysprecipitate in a light, open condition, the plasticizer solutionpenetrates the minutest pores and, upon evaporation of the solvent,leaves the plasticizer intimately and thoroughly incorporated therein.

The same open porous characterof=- the material when produced in anunplasticized condition makes possible the ready incorporation ofplasticizer by either chemical or mechanical means. For example, theplasticizing agent may be ground into the unplasticized granularmaterial or it may be incorporated from a solution thereof, the lattermethod being preferable due to the greater penetration and occlusion tobe thus obtained. In either case the material is in a finely dividedgranular form having the general appearance of well ground wheat flouror of baking soda and lends itself readily to'the inanufacture of alarge variety of molded articles.

In addition to dimethyl and diethyl phthalates other typical examples ofplasticizers suitable for the purposes of our invention aremonochlornaphthalene, triphenyl phosphate, tricresyl phosphate, v ethylacetanilide, ethyl p-toluene sul fonamide.v It is to be understood thatthese are merely intended as examples of some of the best knownplasticizers and it will be obvious that many others may be used withsatisfactory results.

One general rule will also be observed from the above examples, namely,that where the solvent and the precipitant for the cellulose organicester are to be removed from the precipitated molding powder by the useof distillation, the precipitant must have a higher boiling point thanthe boiling point of the-solvent in order that the solvent will bedistilled ofi? first andleave, the precipitant predominating. The reasonior this will be obvious, because if the precipitant were to distill ofifirst, the solvent would soon all predominate to such an extent that thecellulose derivative would go back into solution. Oi course, if themixed precipitant and solvent is filtered oil from the precipitatedcellulose ester,

, uncolloidized form, the particles of which have an open, porous,non-fibrous structure, which comprises dissolving the ester in a solventtherefor,

adding to the solution with vigorous agitation until the ester isprecipitated an organic nonsolventfor the ester having a higher boilingpoint than the solvent, and then subjecting the ester to an increasinglystronger precipitating action by successively evaporating off thesolvent and non-solvent.

2. The process of producing a finely divided 'cel lulose organic estermolding powder oi! uniform composition and particle size in granularuncolloidized form, the particles of which have an open, porous,non-fibrous structure, which com prises dissolving the ester in asolvent therefor, adding to the solution with vigorous agitation untilthe ester is precipitatedan organic nonsolvent for the ester having ahigher boiling point than the solvent, and selected from the groupcomprising toluene, xylene, benzene, methyl alcohol, carbontetrachloride, normalbutyl alcohol, iso-propyl ether, trichlorethylene,butoxy ethyl alcohol, and propylene chloride, and then subjecting theester to an increasingly stronger precipitating action by successivelyevaporating ofl the solventand non-solvent.

3. The process of producing a finely divided cellulose acetate moldingpowder of uniform composition and'particle size in granularuncolloidized form, the particles of which have an open, porous,non-fibrous structure, which comprises dissolving the cellulose acetatein a solvent therefor having a lower boiling point than toluene, addingtoluene to the solution with vigorous agitation until the celluloseacetate is precipitated, and then subjecting the cellulose acetate to anincreasingly stronger precipitating action by successively evaporatingoff the acetone and the toluene.

a. The process of producing a finely divided cellulose acetate moldingpowder 01 uniform composition and particle size in granularuncolloidized form, the particles of which have an open, porous,

non-fibrous structure, which comprises dissolving the cellulose acetatein acetone, addingtoluene to the solution with vigorous agitation in anamount representing approximately a ratio of 3:1 with respect to theacetone, whereby the cellulose acetate is precipitated, and thensubjecting the cellulose acetate to an increasingly strongerprecipitating action by successively distilling oflE the acetone andtoluene.

5. A precipitated, finely divided, granular, uncolloidized organiccellulose ester molding powder of uniform composition and particle size,the particles. of which have anopen, porous, nonfibrous structure, saidpowder being of substantially the same .character as that produced bythe process of claim 1.

6. A precipitated, finely divided, granular, uncolloidized organiccellulose ester molding powder of uniform composition and particle size,the particles of which have an open, porous, nonfibrous structure andhaving a particle size such.

that the powder will pass at least a 40-mesli screen, said powder beingof substantially the same character as that produced by the-process ofclaim 1.

7. A precipitated, finely divided, granular, un" colloidized celluloseacetate molding powder CC uniform composition and particle size, the paricles of which have an open, porous, non-fibrous structure, said powderbeing of substantially the same character as that produced by theprocess oi claim 1.

8. A precipitated, finely divided, granular, uncolloidized celluloseacetate-propionate molding powder of uniform composition and particlesize, the particles of which have an open, porous, nonfibrous structure,said powder being of substantially the same character as that producedbythe process oi claim 1. 1

9. A precipitated, finely divided, granular,,uncolloidized celluloseace'tate-stearate molding powder of uniform composition and particlesize, the particles of which have an open porous, nonfibrous structure,said powder being of substantially the same character as that producedby the process of claim 1.

10. A precipitated, finely divided, granular, uncolloidized celluloseacetate molding powder of uniform composition and particle size, theparticle size being such that the powder will pass a til-mesh screen,and the particles thereof having an open, porous, non-fibrous structureand having a plasticizer intimately incorporated therein, said powderbeing of substantially the same character as that produced by theprocess of claim 1.

DENNIS E. NORTHRUP. AMOS W. CRANE.

